Pump



PUMP

Filed Dec. e, v1954 s she'ets-svheet 1 11W/EMME. Stephen Bukojol ATTO RN EY'S s. BUKATA PUMP 8 Aug. 6, 1957 Filed neme, 1954 Fraga* IN VEN TOR.

Flsfr' s m Mn o N u n A e .nl D. e t S l A, WM

United States arent Gti-ice 2,801,788 Patented Aug. 6, 1957 Bref-1 PUMP Stephen Bukata, Philadelphia, Pa., assigner to F. J. Stokes' Corporation, Philadelphia, Pa., a corporation of Pennsylvania Apparati@ December s, 1954, Samus. 47331292"r 7 claims. (c1. zsm-101)` This invention relates to high-vacuum punnas an'd`in` particular provides a diffusion pump employing a` stagev4 orderof one tenth of a micron and require that the forepressure be pulled down to on the order' of about`200 to 500 microns as a maximum forepressure.

against which it can work, it is common to construct a diffusion pump having a plurality of stages in order to obtain greater pumping speeds` and the production ofY higher vacuums. Pumping speed of any diffusion pump stage, that is, the volume of gas at the inlet pressure of the stage which can be handled in a given time, is largely a function of the crosssectional area of the pumping chamber at the stage, of the width between the pump vapor jet and the pumping chamber wall" and of the amount of pump vapor available at the stage. The width of the spacing of the jet and pumping chamber wall also. limits the forepressure against which the stage cantoiper ate.

Ai very common form of diffusion pump employinga plurality of stages is the Langmuir-Gaede condensation pump in which superposed umbrella jets radiate from a vapor chimney` coaxially contained within the pumpingv chamber. In this arrangement, referring to the first s tage as the stage having the highest vacuum at its inlet, the cross-sectional area of the pumping chamber at the first stage is greatest and decreasesat each stag-e and halso the` distance from the jet to the pumpingV chamber wall-is greatest in the iirststage and decreases `witheach stage. Vapor is directed to the umbrella jet of each stage from a boiler through the vapor chimney on which the jets are mounted. Conventionally the pumping chamber is a conduit, open at its inlet end for connection to thej system tov be evacuated and'provided at its outlet endi'with ai lateral leg which is connected to the forepump. j

In operation the vapor issuing from each umbrella jetl is directed toward the outlet end and condenses on the pumping chamber wall prior to the-next succeeding stage,

or outlet in the case ofthe final stage umbrella jet. The" movement of the pump `vapor molecules toward the out-` let, as is wellknown, drives gases from the system tobe`- evacuated by sweeping thegases present in thepumping chamber toward the outlet. Since the pressures increase toward the outlet end of the pump, the required cross-A sectional area is reduced toward the outlet asf the volume of gas being pumped decreases. At the same time the space between the jetand the wall of the chambernecessarily also decreases because the fcrepre'ssure for each given stage increasesfromv the inlet to theoutlet.

The above considerations dictate the size of a` high'- vacuum Adiffusion pump which is required'to` produce a` given vacuum ata given pumpingwspeed. In general, the

height and bulkwof the'purnp increase as greater pumping:

` Because' the capacityof a diffusion pump is limited by the forepressure' speeds or higher vacuums are secured by the use of a greater number of stages.

I havenow discovered that increased pumping speeds can be" obtained in' high-vacuum diffusion pumps without requiring additionalstages, and conversely, a given pumping sp'eedcan be obtained using a lesser number of stages.

I have also discovered that backstreaming, which'isa' function `of the relative separation of the jet andthe pumping chamber wall in any given stage, can be mm1- rnized and the pressure differential over which a given stage can be operated can be increased without decreasing the pumping capacity of the stage.

These and other advantages I have found can beobtained'by employing a plurality of individual jets in a` speed" and conversely, permitting the achievement of-l greater pumping speeds for a given number of sta'ges.

I' am aware that'it has heretofore been proposed to employ a` plurality of ejector nozzles as a booster pump' or in a final stage of a booster pump.` Such arrangements, however, for example, aslis shown inDowning et al. Patent 2,386,298,` provide for direction of each ejector nozzle into a` diffuser which functions in thefrnan#` ner of an aspirator to pumpY the gas` to be evacuated through-the diffuser by achieving a high velocity` of-purnp vapor through a restricted cross-sectional area'- in" the "diffuser. My invention is to be differentiated from such devices'in that in the plural jet stage which I employ-each` jet directs the pump vapor toward the outlet endfof the diffusion pump chamber in a manner analagous to the operation of thecommon umbrella jet. The vapor stream:

from'each'jet in the plural jet stage of my inventionl ist thus directed into a substantially unrestricted space pro# viding only surface for condensation of pump vapor.

The plural jet stage of my invention is useful iwh'ere' jetdiffuser stages cannot be employed, that is,v as a stage of a high vacuum diffusion pump as well as in a 'booster pump.

The jets which I employ can be conical'or pyramidical in shape, and are usually flared out toward theiropening into the pumping chamber in the direction of flow through the pumping chamber. They can be umbrella jets by the simple expedient of employing a `pluralityor vapor chimneys disposed within the pumpingchamber. The jets `constituting a given stage according to myinvention open into the pumping chamber in approximately a transverse plane through' the chamber. The openings of the jets into the pumping chamber can be circular, triangular, square or any other shape which is desired" to provide a `suitable pattern of jet distribution in the stage. The jets can include a central umbrella jetform-` ing a jet in the same stage of the' pump. Where more than one bank of jets is to be employed `in agiven" stage, a cooled cylindrical, conical, prismatic, pyramidical or other Vsuitable surface can be disposed between adjacent banksof jets to provide additional condensation surface for the pump vapor.

The number of jets in each stage is adjusted to provide chimney is employed which extends past a given Stege of" jets, exclusive of the case where a'central jet such as an umbrella jet is employed, the spacing between the vapor chimney and the jets adjacent to the vapor chimney is the same as the spacing from the outer wall of the pump chamber to the jets adjacent thereto. Jets which are adjacent to a cooled surface or the like, as described above, which is placed in the pumping chamber to provide additional condensation surface are spaced from such surface approximately the same distance as the jets adjacent to the conduit wall are spaced from the conduit wall.

For a more complete understanding of the principles of my invention, reference is made to the appended drawings in which:

Figure 1 is a vertical sectional view of a diffusion pump constructed according to my invention;

Figure 2 is a top view of the same pump as shown in Figure 1;

Figure 3 is a vertical sectional view of another diffusion pump constructed according to my invention;

Figure 4 is a cross-sectional view of the pump shown in Figure 3 taken at line 4--4 in Figure 3;

Figure 5 is a cross-sectional view of the pump shown in Figure 3 taken at line 5 5 in Figure 3;

Figure 6 is a cross-sectional view of the pump shown in Figure 3 taken at line 6 6 in Figure 3;

Figure 7 is a vertical sectional view of yet another diffusion pump constructed in accordance with my invention; and

Figure 8 is a top View of the pump shown in Figure 7.

In the drawings, referring to Figures l and 2, the reference numeral 10 represents an elongated vertical conduit having an annular llange 11 at its upper end for connection to a system to be evacuated and closed at its lower end by a bottom 12. Near the lower end a side conduitV 13 is connected to conduit 19 and is, in operation, connected to a forepump (not shown) of conventional construction.

A boiler 14 is positioned in the lower end of conduit 10. Boiler 14 is enclosed at its top by a vapor chimney 15 which extends coaxially within conduit 10 toward the inlet end of conduit 10 and is provided with conventional means 14a for heating the pump fluid.

Vapor chimney 15 is formed of a lower cylindrical section 16 and an upper conical section 17 capped at its apex 18. The lower end of conical section 17 is supported overlapping the upper end of cylindrical section 16, spaced thereabout to form an umbrella jet 19 of conventional construction. A conical skirt 2t) depends from cap 18 for a short distance over the upper end of conical section 17. A series of openings 21 about the upper end of conical section 17 just beneath its junction with conical skirt define a second umbrella jet 22.

A series of conduits 23 communicating with the interior of vapor chimney 15 are mounted about the perimeter of cap 18 and extend for a short distance toward the inlet end of conduit 10. Conduits 23 are then turned in a radial direction and finally toward the outlet end of conduit 10, ending in slightly ared openings which deline jets 24 for directing vapor from vapor chimney 15 into the pumping chamber between vapor chimney 15 and conduit 10 in a direction toward the lower end of conduit 10 as which outlet 13 is located.

A truncated conical plate 25 is positioned about umbrella jet 22 extending above and below the opening of umbrella jet 22. Plate 25 is supported by outwardly declined spider supports 26 positioned clear of the path of ejection of vapors from jets 24.

The positioning of jets 24 and of plate 25 is best shown by reference to the distances marked off in the drawings. Labeling the transverse measurement across the spacing between each jet 24 and the inner wall of conduit 10 as a distance A, then the corresponding measurement between each jet 24 and conical plate 25 is a distance A, the corresponding measurment between umbrella jet 22 and plate 25 is a distance A, and the corresponding measurement between each adjacent pair of jets 24 is a distance 2A.

Conduit 10 can and usually is provided with a jacket (not shown) in the conventional manner to provide for ilow of a coolant. Similarly, plate 25 can be cooled by providing for flow of a coolant therethrough. The lower end of cylindrical section 16 enclosing boiler 14 is suitably provided with openings 27 for returning condensed pump vapor.

In operation, as indicated above, the inlet end 11 of conduit 10 is connected to a system to be evacuated and outlet 13 is connected to a forepump of conventional construction. Boiler 14 is lilled with a suitable uid for use in a diffusion pump, such as mercury or one of the special oils conventionally employed. Heat is applied to boiler 14 producing vaporization of the liquid. The vapors rise up in vapor chimney 15 and issue from vapor chimney 15 through jets 22, 24 and 19. All of the jets are, of course, directed to cause the pump vapor to issue toward the outlet end of conduit 10. In so moving into the pumping chamber, the molecules of the pump vapor strike the molecules of the gas from the system to be evacuated which have diffused into the chamber enclosed by conduit 10 causing the gas molecules to be driven toward the outlet end of conduit 10 from which they are removed through outlet 13 by the forepump.

The pump vapor from jets 22 and 24 is condensed rapidly on the inner wall of conduit 1) and on the sides of conical plate 25. The condensed pump vapor drains downwardly along the inner wall of conduit 10 and drains from plate 25 down spiders 26 to the inner wall of conduit 10. Similarly, the pump vapor issuing from the second stage jet 19 is condensed on the inner wall of conduit 10 and drains to the lower end of conduit 10 where it re-enters boiler 14 through openings 27.

The pump described in Figures l and 2 will produce the same pumping speed as a three-stage pump working against the same forepump pressure and located in a conduit of the same diameter as conduit 10. The pump shown in Figures l and 2 is also capable of 40 percent greater pumping speed than a comparably sized, twostage pump employing conventional umbrella jets only.

Figures 3 through 6 illustrate a diffusion pump constructed in accordance with my invention employing three plural jet stages.

In the diffusion pump shown in Figures 3-6 the reference numeral 30 represents an elongated vertical conduit having annular flange 31 at its upper end for connection to a system to be evacuated and closed at its lower end by a bottom 32. Near the lower end a side conduit 33 is connected to conduit 30 and is, in operation, connected to a forepump (not shown) of conventional construction.

A boiler 34 is positioned in the lower end of conduit 30 and is provided with conventional means 34a for heating the pump uid. Boiler 34 is enclosed at its top by a vapor chimney 35 which extends coaxially within conduit 30 toward the inlet end of conduit 30.

Vapor chimney 35 is formed of a lower conical section 36 and an upper conical section 37. Upper conical section 37 is formed with a greater apex angle than lower conical section 36 and overlaps at its lower end the upper end of lower conical section 36 in tight engagement therewith. The apex 38 of upper conical section 37 is provided with an opening to admit passage of a bolt 39 which extends through vapor chimney 35 and threadedly engages bottom 32. The end of bolt 39 extending through opening 38 terminates slightly above opening 38 and threadedly receives a knurled nut 40. A spring 41 is retained about bolt 39 between knurled nut 40 and the apex of conical section 37 under suticient compression to hold conical section 37 tightly down upon conical section 36 and in turn to hold conical section 36 tightly upon bottom 32. The lower end of conical section 3G is provided witha series of-openin'gs 421adjaceht to bottom 32, such that liquid draining down the inner walls of`conduit can enter into boiler 34:

At `the apex ofconical section 37 vapor chimney 35 is provided "with four lateral openings from each of which a conduit 43 extends approximately radially outward. Each conduit 43 at its outer extremityl is turned downwardly terminating in a flared jet opening 44,-all four jet openings 44 being positioned approximately in a? plane. The distances from' the `inner'wall of` conduit A30 to the perimeter ofeach opening 44adjace`nt` to the inner wall of conduit 30 are approximately equal and areA approximately equal to the distances from the outer wall of vapor` chimney 'to the perimeter of each opening-44 adjacent to such outer wall,` such distances being measured approximately in a 4plane perpendicular to the axis of conduit 30 in which openin'gsr44slie. Similarly; the distances between: each adjacent pair of openings 44 taken from the most closelyadjacent portionsoftheirperimeters are approximately equal and are approximately equal 'to twice the distances fromsuch openings 44 to thevinner wall of conduit 30 and outer wall of vapor-chimney 35. Open-" ings 44` constitute the rstjet lstage of the pumpshown in Figures 3-6. Their spatial arrangementis mostclearly shown in Figure 4.

The second stage of the pump shownV in iFigures 3 6` includes eleven conduits `45 extending approximately 'radii ally from openings equally spacedabout vapor Chim-1 ney35: located intermediate the ends of conical sectionr 37. Conduits 45'at their outer endsextend downwardly into` ared openings 46,` all of lwhichlie approximately in a plane perpendicular tothe axis lor conduit `30.` The same considerations as to the spacingbf openings 44 witlr respectito each other and with respect to the irinerwall` ofconduit 30 andthe outer wall of vapor'chimney 35 apply' tthe spacing of each adjacent pair of openings 46 and thev spacing 'from each opening 46 to ther inner wall of conduit 30 and to the outer wall of`vaporchimney 35. It will be noted that because'V of the conicalv shape of vapor chimney 35 the totaltansverse area throughwhich gases being evacuatedrcan be passedinf the secondstage of the `pumpV shown in Figures 3-6-is considerably lessthan the total` transverse area at the first stage.` This difference in area is bestl illustrated by comparing Figures 4 and '5 which show most clearly' the spacing of the elements in the rst and secondstages of the pump;

A third' stage located near the lower end-of" conical section 37 of vapor chimney 35` includesr a seriesv of twenty-eight radially extending conduits 47 connected to equally spaced openings in vapor chimney `35`Qand turn-t ing-downwardly at their terminal ends into flared openings 48which open into the chamber between conduit 3d and "vapor'chirnney 35 in approximately aV transverse planethroughrconduit 30. Again the same`- considerations as to the spacing of openings 48 and of the outer wall of vapor chimney 35 andthe inner wall of conduit 30 apply. Again the total transverse area of the stage is reduced. Figure 6 best shows the spatial distribution of jets 48y which constitute the third stage of the pump;

The operation of'th'e pump shown `in Figures 3 6 is essentially similar to the operation of the pump shown in Figures l and 2. Vaporize'd pump fluid from boiler 34 risesT upwardly in Vapor chimney 35 and issues through jet openings 44, 46 and 48 diiusing downwardly in the chamber between conduit 30 and vapor chimney 35 to strike molecules of gas from the system to be evacuated and drive them toward lateral forearm 33. The pump vapor condenses on the walls of the chamber as before and drains back to boiler 34.

A similar three-stage pump of the conventional um- I brella type working against the same forepump pressure would have a highly reduced pumping speed necessitated by the fact that the distance from the umbrella jet to the inner wall of conduit 30 in each stage would have to be approximately equal to the distance between the' most adjacent portion of the perimeter of the openingsf44, `46 or 48; as the case may be', and the inner wall of the conduit 30. Consequently, the` total transverse areal available in each `stage of the prior pumps would necessarily be much less and the volume of gas lwhich'could` bepumped past each'such stage in a given time would accordingly be'reduced.

Thearrangement of the assembly of the vapor chimney shown in Figure 3 is particularly advantageous inthat the spring 41 allows for contraction and expansion of the' vapor chimney elements during heating and cooliugand also for unequal' contraction and-expansion in the event that rod 39` and chimney 35 are constructed in metals having differing coefficients of thermal expansion. At the same time spring 41 and nut 40` hold vapor chimney 3S in place during use and facilitate disassembly for cleaning in between periods of use,- the entire vapor chimney assembly being removable by loosening nut 40 and spring 41, thereafter lifting conical section 37 and conical section 36 separately from their position spaced about rod 39 within conduit 30.

Figures 7` and- 8 show yet-another construction of the diusion pump having'arst and asecond plural jet stage in accordance with my'invention in combination with a third, inal, umbrella jet stage. j

In the arrangement shown in Figures 7 and 8 the reference numeral 50 designatesan elongated vertical conduit having an annular ange 51 at its upper end for connection to a system to be evacuated. Conduit 50 at its lower end is provided with a bottom 52-and a lateralV take-off conduit 53 which is, in operation, connected to a forepump (not shown) of conventional construction.

A boiler 54 is positioned in the lower'end of conduit 50 and is enclosed at its top by a vapor chimney 55. Vapor chimney is constructed of essentially cylindrical conduit 56 resting on" bottom 52 and coaxially positioned within conduit 50. Cylindrical section 56 has supported above it a conical section 57 from which a conical skirt 58 depends overlapping the upper end of cylindrical section 56 in spaced relation thereto dening an umbrella jet 59 of conventional construction. Cap conical section l57 is suitably supported by spiders 60 which connect the inner wall of conduit 50 and skirt 58.

Eight vertical chimney extensions 61 are mounted at equal arcuate distances about the base of conical cap section 57 of vapor chimney 55 and a central chimney extension 62 extends upwardly from the apex of conical cap section 57. Chimney extensions 61 and 62 all terminate at their upper ends in approximately a horizontal plane and are each covered by a dish-shaped cap 63 having its outer edges turned downwardly and which is spaced slightly over the open upper end of each chimney extension 61 and 62 to dene nine umbrella type vapor jets 64; Each dish-shaped cap` 63 at its center supports a chimney extension 65 having a smaller diameter than chimney extensions 61 and 62, is in turn terminated at its upper end in approximately the same horizontal plane as each other chimney extension 65 and is capped by an. inverted dishshaped member 66 which is spaced slightly above with its outer" edges turneddown to define an umbrella jet 67. Dish-shaped caps 66 have a substantially smaller crosssectional area than dish-shaped caps 64.

Extending above and 'below umbrella jets 64 and 67 and positioned coaxially within conduit Sil about central chimney extensions 62-65 and within the ring formed by outer chimney extensions 61--65 is a cylindrical member 68 provided with internal cooling (not shown). Member 68 is connected at its lower end by slanted drip legs 69 to the inner Wall of conduit 50 to drain pump vapor which condenses on its surfaces to the inner wall of conduit 50.

The lower end of cylindrical section 56 enclosing boiler 54 is provided with a series of openings 70 to permit condensed pump vapor to drain back into boiler 54. A con- ^7 ventional heating unit 71 for boiler 54 is positioned beneath bottom S2.

Referring to the plan view shown in Figure 8, it will be seen that the first stage jets 67 in the outer bank are each equally spaced from the inner wall of conduit 50 and the outer cylindrical surface of cylindrical member 68 and that such spacing is approximately equal to the spacing between the edge of the -central jet 67 and the inner wall of cylindrical member 68. It will be further observed that each adjacent pair of jets 67 in the outer bank are spaced apart approximately twice such distance.

The same spacing arrangement necessarily holds for jets 64 in the second stages except that the distances are diminished due to the larger diameter of disc caps 63. This decrease in spacing is, of course, necessary because the stage operates at a greater forepressure. The iinal stage jet 59 is of conventional umbrella type as noted before and its spacing is the annular width between skirt 58 and the inner wall of conduit 50, which is again a smaller distance because of the necessity to operate it at even greater forepressure.

In the pump shown in Figures 7 land 8, operation is essentially as that shown in the previous figures. The first and second jet stages in this instance, however, are operated in accordance with the principles of my invention in combination with a conventional final stage.

The foregoing description is necessarily limited to a few selected examples of diffusion pumps constructed in accordance with my invention. It will be apparent that many other constructions can be made in accordance with my invention. Such variations can include pumps which are in positions other than vertical, pumps having external Vapor chimneys and the like, as well as countless variations in locating the jets which constitute each plural jet stage in accordance with my invention.

I clairn:

l. In a vacuum pump provided with a casing having an inlet at one end for connection to a system to be evacuated and an outlet at the other end, vapor chimney means disposed within said casing for delivering a condensible pump vapor into said casing, wherein the outer surface of said vapor chimney means and the inner surface of said casing define between them a pumping chamber and wherein the transverse dimensions of said casing and said chimney means are selected such that said pumping chamber has a cross-sectional area which decreases towards the outlet end of said casing, the improvement which comprises a pump vapor jet stage in said pumping chamber including a plurality of jets communicating with said vapor chimney means and opening into said pumping chamber in approximately a transverse plane through said chamber, said jets constituting said stage being directed to discharge pump vapor into said chamber toward the outlet end thereof and having their openings into said chamber disposed in spaced relationship from each other and from the inner surface of said casing, and said pumping chamber being substantially clear of structure restricting the path of vapor discharge from said jets.

2. The improvement according to claim 1 in which said vapor chimney means comprises a single vapor chimney coaxially positioned within said casing.

' 3. The improvement according to claim 1 in which said vapor chimney means comprises la single vapor chimney coaxially positioned within said casing and in which one of said jets is a central umbrella jet extending about said vapor chimney.

4. The improvement according to claim 1 in which said vapor chimney means comprises a single vapor chimney coaxially positioned within said casing and in which said jets are disposed in a ring about said vapor chimney with their openings into said' chamber spaced from the outer surface of said vapor chimney.

5. The improvement according to claim l in which said jets include a central jet and a group positioned about said central jet and in which said improvement further includes a plate in the form of a truncated cone interposed in spaced relationship from all said jets between said group of jets and said central jet.

6. The improvement according to claim 1 in which said jets include a central jet and a group positioned about said central jet and in which said improvement further includes a cylindrical plate interposed in spaced relationship from all said jets between said group of jets and said central jet.

7. In a vacuum pump provided with a casing having an inlet at one endfor connection to a system to be evacuated and an outlet at the other end, a vapor chimney disposed coaxially within said casing Vfor delivering a condensible pump vapor into said casing, wherein the outer surface of said vapor chimney and the inner surface of said casing dene between them a pumping charnber having an annular cross-section and wherein the transverse dimensions of said casing and said chimney are selected such that the area of said annular crosssection decreases towards the outlet end of said casing, the improvement which comprises a pump vapor jet stage in said pumping chamber including a plurality of jets communicating with said vapor chimney and opening into said vpumping chamber in approximately a transverse plane through said chamber, said jets constituting said stage being directed to discharge pump vapor into said chamber toward the outlet end thereof and having their openings into said chamber disposed in spaced relationship from each other in a ring concentric with the axis of said vapor chimney and casing and having their openings into said chamber spaced from the inner surface of said casing and from the outer surface of said vapor chimney, the spacing of each of said openings from the inner surface of said casing being approximately equal, the spacing of each of said openings from the outer surface of said vapor chimney being approximately equal and equal to the spacing of said openings from said inner surface of said casing, the spacing of each adjacent pair of said jets in said ring being equal to no more than three times the spacing of each of said jets from the inner surface of said casing, and said pumping chamber being substantially clear of structure disposed between said inner wall of said casing and said outer wall of said vapor chimney in the path of vapor discharge from said jets.

References Cited in the file of this patent UNITED STATES PATENTS 2,237,806 Bancroft Apr. 8, 1941 2,432,226 Cox Dec. 9, 1947 2,447,636 Colaiaco Aug. 24, 1948 FOREIGN PATENTS 801.042 Germany Dec. 21, 1950 

